The present invention is in the field of electrical switches, and more particularly, contactors for high-power direct current (DC) circuits.
In certain circumstances there is a need to interrupt current in a DC circuit while the circuit is carrying a high current (e.g. 50 to 200 amps). These circumstances may arise, for example, when an electrical load on the circuit becomes excessive or when a short-circuit fault develops. In order to accommodate such eventualities, high-current DC circuits may incorporate heavy-duty contactors.
Rapid interruption of current may produce an induced surge of energy. This energy may produce arcing in a contactor. Some heavy-duty contactors may be constructed so that this arcing may be tolerated. Other prior-art contactors may be constructed so that such arcing is reduced.
In some prior-art contactors, a gas-tight or liquid-tight enclosure may be provided for the contactor or its contact elements. A gas or liquid may surround the contact elements and prevent oxidation of the elements when arcing occurs. In other prior-art contactors, selected arc-tolerant metallic alloys may be used for contact elements.
Some prior-art contactors may be provided with an electrical shunt that may by-pass an energy surge around the contact elements. Such a shunt may comprise a high-power field-effect transistor (FET) or similar device. The FET must be able to tolerate a high-current surge without damage. For example, a shunt or by-pass rated at about 1500 amps may be needed for a contactor rated at 150 amps that may be required to open with a “short circuit” condition.
Prior-art high-power contactors with protected contact elements or with by-pass shunts are expensive, heavy and complex. These characteristics of prior-art contactors are of particular concern to aircraft designers. Aircraft designs are evolving in a direction that is often referred to as “more electric architecture” (MEA) design. In new MEA designs various operational functions which were formerly performed with hydraulic and pneumatic systems are now performed electrically. These electrical operations are often performed with high amperage DC motors and controls. In this context, MEA designs may incorporate an increasing number of contactors which may interrupt high-amperage DC. MEA designs could be improved if high-power contactors could be made lighter, less expensive and more reliable than prior-art contactors.
As can be seen, there is a need to provide improved contactors which are capable of interrupting high amperage DC. Additionally, there is a need to provide such contactor with low weight so that they may be effectively employed in aircraft.